Gene therapy, whereby exogeneous nucleic acid is added to a cell to correct genetic defects or to treat disorders, is a rapidly emerging field. Frequently, gene therapy is done uses a patient's cells as the vehicle for the exogeneous nucleic acid; that is, cells may be excised from a patient, genetically manipulated, and reintroduced into the patient. See for example U.S. Pat. No. 5,399,346.
One problem with this approach is that excised cells generally have a finite lifespan in culture, absent further genetic manipulation. Thus, frequently, excised cell lines are transformed with an immortalization gene such as an oncogene. This allows indefinite growth and proliferation of the cells. However, immortalized cells containing oncogenes are unsuitable transplant candidates, due to the undesirability of introducing oncogenes into a patient.
Accordingly, it is an object of the invention to provide methods and compositions for the creation of immortalized cell lines which may be grown and perpetuated ex vivo, and then induced to disimmortalize, that is, remove the oncogenes, before introduction into a patient or animal.